PROJECT SUMMARY/ABSTRACT Organ function may be modulated by stimulating peripheral activity and targeting, for instance, peripheral nerves and autonomic ganglia. However, the detailed functional and anatomical organization is not well understood for autonomic nerves, ganglia and organs involved with visceral functions. Significant knowledge gaps exist with regards to the neural control of many organ functions, including those of the heart, respiratory system, lower urinary tract, and gastro-intestinal system. An improved understanding of the various components of neural circuitries and innervation of peripheral organs is needed in order to provide improved modeling and design of devices to allow for optimal modulation of select organ functions. Transmission electron microscopy (TEM) allows for the identification of the fine structure of neural tissues to characterize, for instance, axonal composition and myelination, organization of neural circuitry in autonomic ganglia, and innervation of autonomic targets. The proposed studies will aim at establishing a TEM service for investigators supported by the Stimulating Peripheral Activity to Relieve Conditions (SPARC) consortium. A total of 6 SPARC-funded projects, which include 7 SPARC-affiliated investigator laboratories, with defined needs for TEM studies have been identified. The projects include studies on the autonomic control of the heart, brain-gut interactions, hypoglossal nerve-influences on respiration, lower urinary tract function, neuro-endocrine regulation of glucose, and modeling of vagal nerve functions. TEM studies will include detailed characterization of myelinated and unmyelinated axons in visceral and somatic nerves as well as organization of autonomic ganglia, and potential synaptic regulation of endocrine functions. Studies will be performed using rodent, large mammal, and human tissues to allow for interspecies comparisons. Sex as a biological variable will also be included in the studies. The TEM service will work closely with each participating SPARC laboratory and provide advice on tissue harvesting and preservation as well as perform tissue processing and embedding of tissues in plastic resin, semi-thin and ultrathin sectioning for ultrastructural studies, TEM of nervous tissues, pre- and post-embedding immuno-EM studies, quantitative analysis of nerves, ganglia, neural circuits, and synaptic structures, customization of TEM protocols to accommodate project specific needs, and interpretation of ultrastructure and quantitative TEM data. It is expected that the proposed TEM studies will add value to SPARC-funded investigations and augment interpretability of functional and modeling studies as well as provide critical ultrastructural data for an evidence-driven approach to the development of new and improved neuro-modulatory strategies.